Remote control system



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SR. NN Nm SNN A Patented Nov. 25, 1947 REMOTE CONTROL SYSTEM George W. Baughman, Swissvale, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application September 4, 1945, Serial No. 614,364

Claims.

My invention relates to remote control systems, and more particularly to centralized traffic control systems for railroads, such for example, as that shown in Letters Patent of the United States No. 2,350,668. issued June 6, 1944, to George W. Baughman and Norman F. Agnew. The principal object of my invention is the provision of improved arrangements for superimposing such systems upon communication line circuits such as a train dispatchers simplex telephone line equipped with selective calling apparatus, in which the line wires are energized in parallel by direct current, to provide a telegraph circuit with earth return.

As disclosed herein, the apparatus of my invention is arranged for use with the selective calling system shown and described in Letters Patent of the United States No. 1,976,548, issued October 9, 1934, to J. C. Field, which employs selectors controlled by impulses of alternately opposite polarity of afrequency of about 3.5 cycles per second.

In the centralized traffic control, or C. T. C. system, a time code is used, comprising short and long impulses and intervals formed by interrupting or varying direct current normally supplied to the line circuit from a central battery, the short impulses being about 0.1 second, and the long impulses about 0.4 second in duration.

The selecting aparatus of each system is nonresponsive to codes transmitted by the other, but the codes of both systems are in a low frequency band which is separated from the voice frequencies by filters and their line signals are incompatible, and to enable both systems to use the same line wires it is the practice to allot the use of the line to only one system at a time, by disabling the C. T. C. system for the duration of a selector code whenever a telephone call is made.

In the C. 'I'. C. system referred to, the length of the territory controllable over a single pair of line. wires is extended by dividing the line into sections each of which provides a battery line circuit for a set of C. T. C. apparatus controlling the usual number of eld stations. The code signals are repeated between the remote section and the office over the line wires of the intervening sections by carrier currents of frequencies above the voice frequency range, using two one way carrier channels for each line section.

In such installations, the selector system usually extends over the entire territory including several C. T. C. sections, and heretofore the selector codes have been repeated from section to section over the low frequency channel involving the disablement of the C. 'I'. C. apparatus for all sections in order to effect the operation of a selector located in any section, with the result that the eiiiciency of the C. T. C. system is impaired to an undesirable extent.

In accordance with a feature of my invention, the selector system is sectionalized to correspond with the C. T. C. system, and the selector codes for each remote section are transmitted from the office over the carrier current transmitter, in lieu of opening the connections to the line battery, interchanges the connections of two of the resistors to form a Wheatstone bridge, placing the two line wires at the same potential, or at a reversed potential, to quickly release the line relays at the C. T. C. stations, but without interference with the telegraph channel even in the case of faulty contact operation, thereby resulting in improved operation of both systems.

I shall now describe one form of apparatus embodying my invention and shall then point out the novel features thereof in claims.

Referring to the accompanying drawing, the reference characters YI, ZI and Y2, Z2 designate the line wires of a dispatchers telephone line which extends from the dispatchers office, shown at the left, through the territory controlled by the C. T. C. system. For simplicity, only two sections are shown, and the line is subdivided in accordance with the requirements of the C T. C. system by interposing a transformer or high pass filter 2| in the telephone circuit arranged to pass currents in the voice frequency range only.

The control machine for the C. T. C. system is assumed to be located at the dispatchers office, but since a showing of but one set of C. T. C. apparatus is deemed suiiicient to illustrate my invention, I have shown herein only that which is associated with the C. T. C. line circuit for one remote section, comprising the line wires Y2-Z2. This circuit is normally supplied with current from a line battery connected across the line wires Y2--Z2 through a remote line unit including a transmitter relay T2 and a receiving line relay IR, the current from battery 80 being effective to maintain energized aline relay R connected across the line wires at each of a plurality of similarly arranged C. T. C. stations, of which for simplicity but one is shown. Each line relay R controls coding apparatus selectively responsive to control codes supplied to line Y2Z2 by the periodic operation of relay T2, and each C. T. C. station is provided with a transmitter relay T, which by connecting the line wires together periodically to vary the current supplied thereto by battery 80 is adapted to transmit indication codes to which the inductively coupled relay IR of the remote line unit is responsive. The line wires YI-ZI are arranged as required for the transmission of coded carrier currents between the oilice and the remote line unit location by the .provision of suitable low pass filters 22 and 22a at the ends of the carrier current section, which block the passage of carrier currents but which have a cut-oil above the voice frequency range.

The carrier current apparatus includes an eleotronic oscillator OSCI at the oice, adapted to generate current of a frequenti7 fl, 'which has its output terminals connected to .the line wires through resonant circuit elements but normally short circuited by a back .contact a of a relay TP, which relay is a repeater of the transmitter relay OT of the C. T. C. coding unit at the oi'ce for the line section Y2`Z2. Relay TP responds to each operation of relay OT in transmitting a control code to remove the short circuit allowing the oscillator OSCI to deliver a code impulse -of frequency fl to the line wires YI-ZL 'and at the same time relay TP operates the Aassociated line relay OR of the `oiiice coding unit locally to `register the transmitted code and to govern its transmission in the usual manner.

At the location of the remote line unit, the code of impulses of frequency fl is received through selective circuit elements and an amplifier AMP! by a code responsive receiving relay CR, which controls two transmitting relays T2 and T3. Relay T`2/ functions when a connector relay CB is energized, as shown, to repeat the code as battery current variations in line Y2--Z2, to which Ythe station line relays R respond. `Relay T3 is not part of the C. T. C. system, but functions as a pole `changer to repeat selector codes into line Y2-Z2 when the connector relay CB is released, as hereinafter described. A second electronic oscillator OSCZ similar to OSCI but at the remote line unit location is arranged to supply current of frequency f2 to the line wires Yl-'ZI in a similar manner, its output terminals being normally short circuited by contact a of relay IR. The periodic operation of relay IR in 'response to an indication code transmitted by relay T at any C. T. C. station in the section is repeated as impulses of frequency f2 over line YI--Zi, and is received at the oce through an amplifier AMPZ by which the line relay OR of the oiiice coding unit is rendered responsive to the code.

It will be seen therefore that carrier currents are supplied to line YlmZl only during code transi mission. Line Y2-Z2, however, is normally energizeol by direct current and it is to be understood that the C. T. C. system is so arranged that a station is enabled to initiate code transmission only when the line circuit has been steadily -energized for a time which exceeds the length of any of the elements of a code, suitable arrangements being provided for transmitting codes initiated at the same time, by diierent transmitters, one at atime in a given order of code superiority. Moreover, if the'line circuit is interrupted during the transmission of an indication code, the interrupted code is retransmitted in its entirety when the line circuit is restored. Each control code begins with an impulse of about 0.4 second duration, and each indication code with one of about 0.12 second duration, 'and in the event a control code and an indication codeare initiated at approximately the same time the former prevails, the station coding `unit being conditioned by the long first impulse to receive the control code, its transmitter becoming disconnected and the code which it started to transmit is stored for transmission later.

Considering now the C. T. C. system circuits in detail, relays TP, CR and R are of the quickacting biased polar type relays OR and IR are of the stay-whereput stick polar type, and the remaining relays are neutral relays, certain of which are slow-to--release as indicated by a vertical arrow through thcir contacts as shown.

In the remote line unit, a slow release connector relay CB is normally energized over a circuit eX- tending from one terminal B of a suitable local source of current Aatcontact a of a manually operable switch El?, over back contacts a of relays CRand CA through relay CB to the other terminal C of the same source. Relay IR normally is in its lefthand position as shown, where its contact b completes an energizing circuit for a slow release relay NS which is thereby kept normally energized, the remaining relays o1 'the remote line unit normally occupying their released positions, as shown.

4The C. T. C. line circuit may be traced `from the positive terminal of battery til over a current limiting resistor 5, and in parallel therewith, a resistor and back contact a of relay T2, thence over one winding of an impulse transformer dil, back contact b of a pole ychanger relay PC, front contact 'h of relay CB and the coils of a low pass filter 23 to line Y2. At each station a circuit extends from line Y2 to line Z2 through the coils of a similar filter 23a over back contact lc of relay M through a resistor S and the winding of relay R, back contact y' of relay M, conta-ct a of a disconnect relay RPP, and the coils of filter 23a to line Z2. The line circuit extends from wire Z2 to the negative terminal of battery ad over a path similar to the one just traced, but including resistor 3 and in parallel therewith, resistor 'i and back contact 'b of relay T2.

The normally energized connector relay CB is arranged to have a release period of about V1,'5 seconds, by the provision of timing means comprising a condenser oi relatively large capacittT connected across its terminals, as shown, and so remains in its energized position when relay CR is responding to a control code transmitted from the oiiice, as well as when relay 1R is responding to an indication code transmitted from a C. T. C. station, and thus maintains the connection of battery to the line wires over its front contacts b and d during the normal operation of the C. T. C. system.

An indication code is initiated at a C. T. C. station by energizing a master relay M, which causes the associated transmitter relay T to be operated periodically in accordance with the code. When relay M picks up, its contacts 7' and lc reverse the connections of the associated relay R to the line, thereby releasing relay R, since this relay is of the biased polar type responsive to current of one polarity only. Relay T picks up and closes its front contact b, connecting line wires Y2 and Z2 together through the coils of filter 23a, and short circuiting relay R, the circuit of which has a relatively high resistance, and the resulting increase in line current through transformer 40 induces an impulse in its seco-ndary winding to operate relay TR to reverse.

Relay IR then energizes the pole changer relay PC over a circuit extending from terminal B at the right-hand Contact b of relay CR, contact b of relay NS, contact c oi relay IR through relay PC to terminal C. Relay PC energizes a slow release relay PCP, over the circuit from terminal B at contact b of relay IR, contact g of relay PC through relay PCP to terminal C. Relay PCP energizes a slow release relay NP over contacts a of relays NS and PCP, and relay NP energizes a slow release repeater relay NPP.

Contacts b and d of relay PC reverse the polarity of the current supplied by battery 80 to line wires Y2, Z2, thereby releasing relay R at each C. T. C. station except the one which initiated the code, thereby disabling the transmitters at such stations.

Relay IR is held reversed while the line polarity is being reversed over a local circuit including front contact e of relay PC and back contacts c of relays NP and NPP, and the transformer 40 is short circuited, until relay NP picks up, over front contact c of relay PC and back contact b of relay NP.

Relay IR, and relay R at the transmitting station, are now under the control of the transmitter relay T at that station. Relay R is energized over back contact b of relay T each time relay T releases during the delivery of the code, and the resulting decrease in line current operates relay IR to normal through transformer 4Q. Each time relay IR reverses, the opening of its contact a allows current of frequency f2 to be supplied to line YI-ZI, operating relay OR to reverse, and each time relay IR closes its contact a relay OR is operated to normal, relay IR operating suitable decoding and code registering apparatus at the oilice in the usual manner.

Relays CB, NS, PC, PCP, NP and NPP remain picked up during the transmission of an indication code by relay T, relay PC being held energized over a stick circuit extending from terminal B at contact b of relay CR, contact d of relay NP, and contact a and the winding of relay PC to terminal C.

Itis to be understood that the office coding unit controlled by relay OR functions in such a manner that the reception of a complete indication code is Veried by the momentary energization of relay OT on the last step. This results in the energization of relay TP, to transmit an impulse of frequency fI over line YI-ZI to briefly energize relay CR, thereby releasing relay PC and deenergizing relays PCP, NP and NPP controlled thereby and restoring the polarity of the current supplied to line Y2--Z2 to normal. While this occurs relay IR is held in its normal position over a local circuit including back contact f of relay PC and front contact a of relay NPP, and transformer 40 is short circuited over back contact c of relay PC, and front contacts b of relays PCP and NPP. Relay M at the transmitting station is released at substantially the same time, and it follows that, upon the release of relay PC, relays R at all stations become steadily energized and the office line relay OR remains in its normal position, restoring the system to its normal condition.

A control code is initiated by energizing the master relay OM at the oice, causing relay OT and its repeater relay TP to be operated periodically to deliver a code of impulses of frequency fI to line YI-Z I to which relay CR responds.

In response to the rst impulse of a control code, relay CR closes its left-hand Contact b, energizing relay PCP, which energizes relays NP and NPP, relay PC remaining released.

The transmitter relay T2 is energized over the left-hand Contact a, of relay CR, to repeat the code into line Y2--Z2. It will be seen that when relay T2 is energized, the connections of resistors 6 and 1 to the line wires are interchanged and that resistors 6 and 8 are connected in series across the two end terminals of battery over front contact a of relay T2, and resistors 5 and 'I are connected in series across these terminals over front contact b of relay T2. Assuming rst that all four resistors are of equal value when relay T2 is picked up, wires Y2 and Z2 are connected to battery 80 at points of the same potential, reducing the line current to zero and releasing the line relays R. The resistors 5--8 also provide a discharge path for energy stored in the line, due to line capacity, or to the inductance of the relays R, which path has two branches, one extending from wire Y2 to wire Z2 over resistors 5 and 6 in series, and the other over resistors 'I and 8 in series.

Considering this circuit from another point of view, it will be seen that the line current includes a steady component of normal polarity supplied over resistors 5 and 8, and that the contacts of relay T2 serve as a pole changer to superimpose thereon acomponent of reversible polarity, over resistors 6 and 'I, the total line current being the sum or diierence of the two components, depending upon the position of relay T2,

In general, it is desirable to arrange the line circuit so that the line relays will release quickly when the transmitter relay picks up and t0 pick up quickly when the transmitter relay releases, to avoid code distortion. For certain types of line circuits the transmission characteristics may be improved by making resistors 5 and 8 of higher value than resistors 6 and 'I, in which case when relay T2 picks up the component of line current of reverse polarity may be made suiiicient to overcome not only the steady component referred to but also the transient discharge current which otherwise would continue to iiow through the line relay windings due to their inductance or due to the capacity of the line to render them slow to release.

Considering now the telegraph circuit which as shown extends between terminals XI and X2 over the usual simplex connections and the line wires of the dispatchers telephone circuit in parallel, and for which a by-pass is required around the interposed lter 2I. The telegraph ii circuit may be traced from terminal XI through thence over the four resistors 5 to 8 in parallel and diierentially through the coils of transformer 4l?, back contacts b and d of relay PC, front contacts b and d of relay CB, and the coils of lter 23 to line wires Y2 and Z2, and through transformer 2 Ia to terminal X2.

It will be seen that the resistance presented by resistors 5, 6, 'I and 8 to the telegraph circuit is one-fourth that which they present to the C. T. C. line circuit and has the same value irrespective of whether relay T2 is picked up 0r released, or is in its mid stroke position in which its front and back contacts are adjusted to overlap, In the event of faulty adjustment or of a failure of the contacts of relay T2, resistors 5 and 8 in parallel maintain the continuity of the telegraph circuit with but a slight increase in its overall resistance not detrimental to its operation. Furthermore, the increase in the resistance of the telegraph circuit due to the series connection through battery 8U is much less than if the alternative bridged form of simplex connection, as illustrated by transformer 2Ia, were used with transformer 2I, since the latter if applied to transformer 2| would require resistors of relatively high value.

It will be seen therefore that the bridge form of transmitting circuit as illustrated by the resistors 5 to 8, improves the operation of both the telegraph and C. T. C. systems over the arrangements heretofore available.

Returning now to a consideration of the control code being transmitted by relay T2, it will be seen that the line relays R will respond thereto in the same manner as when the line circuit is periodically interrupted as in the prior systems. Relay PCP is energized periodically by relay CR, and relay NPP controlled thereby remains picked up until the code is completed. Transformer l0 is short circuited over back contact c of relay PC and front contacts b of relays PCP and NPP, and the impedance it presents to the line circuit is thereby reduced. Relay IR is held in its normal position throughout the code by the energization of a local winding over the circuit including front contact a of relay NPP and back contact f of relay PC.

The dispatchers telephone system includes a telephone at the office and at each of a number of way stations at each of which a selector is provided for selective ringing, which may be of the type shown in Letters Patent of the United States No. 1,343,256, issued June 15, 1920, to J. C. Field. For simplicity but one selector is shown in each line section, identified by the references SEI and SEZ, respectively, these being selectively responsive to codes delivered to the line wires by a transmitter of the type shown in Patent No. 1,976,548, hereinbefore referred to. Each selector code comprises a series of seventeen impulses arranged in three groups in accordance with the table of code settings contained in this patent, and to effect their transmission, the selector code transmitter is provided with two rows of numbered push buttons. It is to be understood that the operation of any button in the upper row selects for transmission the first digit, and the operation of one in the lower row, the remaining digits of a code, by making the proper connections to a series of coding segments. The operation of the keys 2, 2', for example, selects the code 2-I3-2. The operation of any key in the lower row momentarily closes a contact S to energize a locking relay 8G, thereby energizing a constant speed motor m to drive a wiper arm or brush connected to one terminal B of the local source of current over each of the coding segments in turn to generate the selected code by effecting the periodic energization of a circuit including wire ll, relay 86 releasing to stop the motor after one cycle of operation.

If the selector code is one for operating a selector SEII', connector relay JBI is energized by relay 86 for the duration of the code to connect a battery 26 over the contacts of a pole changer relay JPC to the primary of an impulse transformer 24 to supply a code of impulses of alternately opposite polarity to the line in accordance with the periodic energization of relayJPC over wire 11, to which code one of the selectors SEI is selectively responsive.

To control the selectors SEZ, the transmitter is modified in accordance with my invention by assigning codes having certain first digits, say 2 or 3, to the selectors in line Y2-Z2, and different rst digits, say 4 or 5, to those in line YI--ZI, and

by the provision of a relay 2-3P which becomes energized when any key in the upper row which controls a selector in line Y2-Z2 is operated. Thus if keys 2 and 2 for the code 2--I3-2 are operated, relay 2-3P is operated by key 2, and relay 86 by key 2 to energize a connector relay JBZ in place of relay JBI. Contact b of relay JBZ then disconnects relay TP from the C. T. C. coding unit and connects it to wire TI, relay JPC being disconnected by the opening of back contact a of relay JBZ. Contact yc of relay JB2 shifts the connections of contact a o-f relay TP so as to reverse the phase of the carrier current code supplied thereby, and since relay TP is released, the immediate effect of the shift is to remove the short circuit from the output terminals of oscillator OSCI, causing current of frequency fI to be supplied to the line to energize relay CR. At the same time, front contact d of relay JBZ completes a local circuit to energize relay OR in the reverse direction, and the opening of back contact d of relay JBZ disconnects terminal B from a wire 2l which it is to be understood disables the C. T. C. office coding unit and interrupts the transmission or reception of a code thereby if one is in progress at the time.

The selector code transmitter is so arranged that following the energization of relay 86, a time interval of about two seconds elapses before motor m connects terminal B to the segment for the first digit of the selector code to effect the energization of relay TP over wire TI. As the operation of motor m continues, relay TP is energized periodically to interrupt the carrier current in accordance with the code setting. Each selector code supplied to line YI-ZI thus begins with a preliminary impulse of about two seconds duration, terminated when relay TP picks up, and is thus distinguishable by code character from a C. T. C. code, in which the duration of the first impulse is of the order of 0.4 second or of 0.12 second as already explained.

The energization of relay CR by the preliminary impulse of the selector code as above described causes relay T2 and the pole changer relay T3 connected in parallel therewith to become energized, for a corresponding period of two seconds. Relay T2 releases the C. T. C. station line relays R and the timing relays which they control, thereby disabling the C. T. C. station transmitters and interrupting any code then in progress. Relay CR also energizes relays PCP, NP and NPP and opens the energizing circuit for relay CB.

Relay CB releases after about 1.5 seconds, completing a circuit at its back contact c extending to terminal B at contact a of relay NP, to pick up a slow release relay CA, which relay opens its contact a in the circuit for relay CB so as to hold relay CB released during the reception of the selector code by relay CR. When relay CB releases, its back contacts b and d disconnect line wires Y2-Z2 from battery 80 and connect the secondary of an impulse transformer 25a thereto, and its back contact a connects a battery 26a over the pole changer contacts of relay T3 to the primary of transformer 26a. Relay T3 repeats the selector code received by relay CR, and causes a corresponding code of impulses of alternately opposite polarity to be supplied to the line wires Y2- Z2, to which code one of the selectors SEZ is selectively responsive.

While relay CB is in its released position, a bypass for the telegraph circuit around transformer 2| is provided which extends from line YI-ZI through coil 25 to the primary oftransformer 24a and thence over back contacts band d of relay CB to line Y2-Z2. These contacts are of the transfer type whereby the continuity of this circuit is maintained during their operation from one position to another.

The last element of vthe selector code constitutes an extended ringing period during which relay TP remains released to supply carrier current to the line. The ringing period is terminated by the release of relays 86, JB2, CR, T2 and T3, whereupon relays PCP, NP vand CA release successively, relay CB then becoming energized to restore the C. T. C. system to its normal condition. Any C. T. C. code which was interrupted due to the transmission of the selector codev will then be retransmitted in its entirety, suitable arrangements for eiiecting vthis result being described in Letters Patent of the United States No. 2,332,191, issued October 19, 1943, to George W. Baughman and Norman F. Agnew, and in a pending application for Letters Patent of the United States, Serial No. 496,907, filedJuly 31, 1943, now U. S. Letters Patent 2,411,375 granted Nov. 19, 1946 by Arthur P. Jackel for Remote control systems. Y l

In practice, the C. T. C. stations of the system are generally equipped with disconnecting apparatus such as is shown in` my Letters Patent of the United States No. 2,376,569, issued May 22, 1945, for Remote'control systems, and illustrated by the relay RPP shown herein. Itzis to be understood that relay RPP releases in kresponse to a steady deenergization of the line YZ--ZZ for an interval of not less than siX seconds, and may be released by energizing relay TP bythe operation orakey K at the ofce to apply steady-current of frequency fl to line Yl-ZL The purpose of relays RPP is to disable the station transmitters in case of a fault in such a way that they may be restored to operation one by one by the transmission of control codes. Since the release period of relay RPP exceeds that of relay CB by a considerable margin, relay RPP is not released during the preliminary impulse of a selector code, while during the delivery of the selector code to line Y2- Z2, each line relay R is operated momentarily by those alternate impulses of the selector code which are of the proper polarity, so that relay RPP is maintained picked up. On the other hand, although when key K is held closed, relay CB releases, this does not interfere with its control of relay RPP. This feature of the system therefore functions in the normal manner when used with the apparatus of the present invention.

It is also of advantage to provide emergency means for calling stations in line YZ-ZZ in order to control trai-lic movements if for any reason the C. T. C. system is out of service. This is accomplished as shown herein by the provision of the emergency keys El and E2, together with a stick polar relay PR connected across line Yl--Zl as shown. When switch El is placed in its upper position, relay 2-3P is non-responsive to the operation of push button 2 or 3, and then all of the selector codes are supplied to line YI-Zl. When the switch E2 is placed in its upper position, relay T3 is connected to the normal contact of relay PR and terminal B is disconnected from contact a of relay CR, causing relay CB to release and allowing the selector codes received by relay PR from line YI-ZI to be repeated by relay T3 into the line section YZ-ZZ, in which case any code having its rst digit 2 or 3 will selectively operate the corresponding selector SEZ located in that section.

Although I have herein shown and described only one form of apparatus embodying myinvention, it is understood thatvarious changes and modications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention,

Having thus described my invention, what I claim is:

1. In combination with a line circuit comprising tw-o sections, a remote control system transmitter and a selector code transmitter located at a control office adjacent a rst section of said line circuit, means for supplying codes of im'- pulses to said. rst section when either of said code transmitters is set into operation, each code transmitted by the selector code transmitter beginning with a preliminary impulse longer than any impulse in a code transmitted by the remote control system transmitter, remote control apparatus located in a second section of said line circuit and responsive to codes of impulses of current of a given character supplied thereto, a selector located in said second station responsive to codes of impulses of current of a different and interfering character supplied thereto, a repeating relay controlled over said first section and normally effective to repeat the codes supplied thereto into said second section as impulses of current of the character to which said remote control apparatus is responsive, and timing means selectively responsive to the reception by the repeating relay of said preliminary impulse to render such relay effective to repeat the succeeding code intosaid second section as impulses of current of said diierent character to which said selector is responsive.

2. In combination with a line circuit comprising two sections, a connector relay, arst code transmitter arranged to supply codes of impulses of current of a given character to one section of said line circuit over normally closed contacts of said connector relay, a second code transmitter arranged to supply codes of impulses of current of a dilerent but interfering character to said one section over normally opencontacts of said con nector relay, a code responsive relay controlled by codes of impulses transmitted over another section of said line circuit for actuating said code transmitters, means controlled by said code responsive relay for actuating said connector relayv to open said normally closed contacts and thereby disconnect said rst code transmitter from the line wires of said one section and to close said normally open contacts and thereby connect said second code transmitter thereto, in response to the rst impulse of a received code, provided such impulse is of a predetermined duration, and slow acting relay means responsive to the continued code operation of said code responsive re lay for maintaining said connector selay in its actiuated position during the transmission of such co e.

3. In combination with a line circuit comprising two sections, a connector relay, two code transmitters one of which is adapted to supply codes of impulses of current of a given character to one section of said line circuit when the connector relay is in a, rst position and the other to supply codes of impulses of current of a different character to said one section when the connector relay is in a second position, a code responsive relay controlled by codes of impulses transmitted from a distant point over another section of said line circuit for actuating said code transmitters and said connector relay, and timing means for selectively controlling said connector relay to render one code transmitter or the other effective to supply a code to said one section, depending upon the relative length of the first impulse of a code received by said code responsive relay.

4. In combination with a line circuit comprising two sections, a repeating relay responsive to codes received over a rst section of said line circuit, a slow release relay arranged to become energized when no code is being received by said repeating relay and to be released when said repeating relay responds to a received impulse of predetermined length greater than that oi any l of the impulses of the codes supplied to said rst section, a rst code transmitter elective when said slow release relay is in its energized position to repeat the operation of said repeating relay for supplying codes of impulses of current of a given character to a second section of said line circuit, a secondvcode transmitter effective when said slow release relay is in its released position to repeat the operation of said repeating relay for supplying codes of impulses of a different character to said second section, two code transmitters operable only one at a time to supply code impulses to said rst section to operate said repeating relay, and means for supplying an impulse of said predetermined length to said iirst section preceding each code transmitted by one of said two code transmitters.

5. In combination with a telephone line divided into two sections by a filter to provide a through telephone circuit and having call selectors in each section, a remote control system having a code 12 transmitter at. a control office adiacent one of said sections and having a transmitter relay controllable thereby to supply codes of carrier current impulses to the line Wires of said one section, a code responsive relay controllable by said impulses for supplying codes of direct current impulses to the line wires of a second section of said line to which a line relay at a station in said section is responsive, a selector code transmitter at said oflice for generating codes of impulses to which said selectors are responsive, means effective if said selector code transmitter is set into operation to generate a code ofV the character to which a selector located in said second section is responsive for effecting the transmission of such code overr the line wires of said one section by carrier current impulses to operate said code responsive relay each such code beginning with a preliminary impulse of longer durationy than any impulse of a code supplied by said remote control system transmitter, and timing means selectively responsive to an impulse of said longer duration received by said code responsive relay for conditioning the code responsive relay to supply impulses of current of a character to which the selectors are responsive in lieu of said direct current impulses to the line wires of said second section.

GEORGE W. BAUGHMAN.-

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,303,875 Baughman Dec. 1, 1942 2,208,446 Baughman July 16, 1940 

